1. Field of the Invention
The present invention relates to a novel photosensitive resin composition. The present invention further relates to an ink-jet recording head using the photosensitive resin composition and a production method for the same. In particular, the present invention relates to a method of improving adhesion between a substrate having a pressure generating element formed thereon for ejecting ink, and a flow path forming member for forming an ink flow path by being bound with the substrate, and a formation method for an ink supply orifice for supplying the ink to an ink flow path by passing through the substrate.
2. Related Background Art
Various proposals have conventionally been made on a production method for an ink-jet recording head, and a liquid path forming member that forms a liquid path by being bound with a substrate having an ink ejection pressure generating element formed thereon. Japanese Patent Application Laid-Open No. 57-208255 and Japanese Patent Application Laid-Open No. 57-208256 each disclose a method of forming an ink-jet recording head by forming a liquid path pattern on a substrate having an ink ejection pressure generating element formed thereon using a photosensitive resin, binding a top board made of glass or the like with the substrate, and cutting the assembly.
Hewlett-Packard Journal 36, 5 (1985) discloses a method of manufacturing an ink-jet recording head by forming a liquid path pattern on a substrate having an ink ejection pressure generating element formed thereon using a photosensitive resin, and adhering an orifice plate prepared by Ni electroforming to the substrate.
Japanese Patent Application Laid-Open No. 61-154947 discloses a method of manufacturing an ink-jet recording head by forming a liquid path pattern on an ink ejection pressure generating element on a substrate having the ink ejection pressure generating element formed thereon using a soluble resin, coating the pattern with an epoxy resin or the like, curing the resin, and eluting the soluble resin after cutting the substrate.
Japanese Patent Application Laid-Open No. 3-184868 discloses that a cationic polymerization cured product of an aromatic epoxy compound is useful for a coating resin composition most suitable for the production of the ink-jet recording head described in the above-mentioned Japanese Patent Application Laid-Open No. 61-154947.
In either of the above-described methods, the binding strength between the substrate having an ink ejection pressure generating element formed thereon and the liquid path forming member basically depends on adhesion of a resin material (photosensitive resin layer, coating resin layer) constituting a liquid path forming member.
Further, in either of the above constitutions, it is necessary to equip a head with an ink supply system for supplying ink. A structure in which a through-hole is formed on a supporting substrate to supply ink from the back of the supporting substrate is generally known in a so-called side shooter type ink-jet recording-head having a structure in which an ejection orifice of ink is arranged so as to face a pressure generating element. Known examples of a production method for such an ink-jet recording head include a method including, as described in U.S. Pat. No. 5,478,606, (1) a step of forming an ink flow path pattern on a substrate having an ink ejection pressure generating element formed thereon using a soluble resin, (2) a step of dissolving a coating resin containing a solid epoxy resin in a solvent at room temperature, and conducting solvent coating of the resultant solution on a soluble resin layer, thereby forming a coating resin layer as a liquid path forming member constituting ink flow path walls on the soluble resin layer, (3) a step of forming an ink ejection orifice on the coating layer above the ink ejection pressure generating element, and (4) a step of eluting the soluble resin layer.
In the case of a so-called bubble jet recording head in which an exothermic resistor is used as an ink ejection pressure generating element and the ink is ejected utilizing bubble formation due to film boiling of the ink, an inorganic insulating layer such as SiN or SiO2 and an anti-cavitation layer such as Ta are generally provided on the exothermic resistor in order to reduce electrocorrosion by ink or damages caused by cavitation in defoaming of bubbles. However, because the Ta film has an extremely low adhesion to a resin material constituting the above-described liquid path forming member, the problem may arise in that the liquid path forming member peels off from the Ta film.
To avoid this problem, it is considered to remove the Ta film on the region on which a resin material constituting a liquid path forming member is provided, for the purpose of improving adhesion of the resin material constituting a liquid path forming member. In this case, however, the resin material constituting the liquid path forming member is laminated on the region on which an electrode connecting to an ink ejection pressure generating element comprising an electrothermal converting material on a substrate is disposed, through only the above-described inorganic insulating layer. Because an inorganic insulating layer such as SiN or SiO2 generally has a porous film material, there is the possibility that ions contained in the resin permeate through the inorganic insulating layer and an electrode is corroded by the ions.
Further, an example is known, in which a substrate is subjected to silane-coupling treatment or an undercoat (adhesion improvement and passivation layer) including a polyimide (for example, PHOTONEECE, trade name, produced by Toray Industries) is used, in order to improve adhesion between the substrate having an ink ejection pressure generating element formed thereon and the liquid path forming member.
The ink-jet recording head generally has a portion that always contacts with the ink under its use environment. It must be avoided that the substrate having formed thereon an ejection pressure generating element is peeled from the liquid path forming member due to the influence of the ink. On the other hand, increasing demands for paper selectivity, water resistance of an image, and the like are made on a recent ink-jet recording system. To meet those demands, studies are being made of the possibility of shifting pH of the ink to the alkaline side. In such alkaline ink, it is sometimes difficult to maintain adhesion between a substrate having formed thereon ejection pressure generating element and a liquid path forming member over a long period of time.
In view of the above, the inventors of the present invention proposed a method of binding a substrate having an ink ejection pressure generating element formed thereon and a liquid path forming member through an adhesion layer made of a polyetheramide resin in U.S. Pat. No. 6,390,606. The inventors had found that according to this method, excellent adhesion of an alkaline ink can also be maintained over a long period of time, and further an ink-jet recording head can be provided which has high reliability that can maintain excellent adhesion over a long period of time even in the case where a metal surface such as Ta is exposed on an adhesive face.
Moreover, various methods such as cutting, sandblasting, laser beam machining, and wet etching are attempted as a method of forming through-holes constituting ink supply orifices on a substrate. However, the methods such as cutting, sandblasting, and laser beam machining involve the problems in that damages to a substrate or each constituent member are large, and in the worst case, a substrate may break during processing.
The wet etching is known as a method of forming through-holes without applying mechanical force to a substrate. The inventors of the present invention proposed a method of forming an ink supply orifice by using a silicon substrate as a substrate, using an inorganic dielectric film and a polyetheramide resin as masks, and conducting anisotropic etching to the silicon using an alkaline etchant in U.S. Pat. No. 6,379,571. According to this method, it is possible to form through-holes without applying mechanical force to a substrate.
Thus, the polyetherimide resin has excellent alkali resistance, and is therefore an excellent material as a constituent material of an ink-jet recording head which contacts with the alkaline ink and also as a mask material in conducting wet etching using an alkaline etchant. However, further improvement is demanded for the polyetheramide resin used for the above applications. Specifically, the polyetheramide resin does not have a photosensitivity by itself. Therefore, when the polyetheramide resin is subjected to patterning, it is required that a photoresist is subjected to patterning to form a mask material, and then patterning is conducted by etching. Further, it is difficult to apply wet etching to the polyetheramide resin. As a result, dry etching must be conducted, and this increases steps and requires large-scaled equipment.